Hilo

Today: Sunny in the morning, then mostly cloudy with scattered showers and slight chance of thunderstorms in the afternoon. Highs around 79 near the shore to 61 to 67 at 4000 feet. North winds up to 15 mph shifting to the northeast in the afternoon. Chance of rain 50 percent.

Tonight: Mostly cloudy. Showers likely and slight chance of thunderstorms early in the evening, then occasional showers and slight chance of thunderstorms in the late evening and overnight. Lows around 61 near the shore to around 47 at 4000 feet. North winds 10 to 15 mph shifting to the northwest after midnight. Gusts up to 35 mph. Chance of rain 90 percent.

Wednesday: Mostly cloudy. Occasional showers and slight chance of thunderstorms. Locally heavy rainfall possible in the afternoon. Highs around 77 near the shore to 62 to 67 at 4000 feet. West winds 10 to 15 mph shifting to the east in the afternoon. Chance of rain 90 percent.

Kona

Today: Sunny in the morning, then cloudy with showers likely and slight chance of thunderstorms in the afternoon. Highs 77 to 82 near the shore to around 67 near 5000 feet. Southwest winds up to 10 mph. Chance of rain 60 percent.

Tonight: Mostly cloudy early in the evening then becoming mostly clear. Showers likely and slight chance of thunderstorms early in the evening, then slight chance of thunderstorms and isolated showers in the late evening and overnight. Lows 61 to 67 near the shore to around 48 near 5000 feet. Northwest winds around 10 mph shifting to the northeast up to 10 mph after midnight. Chance of rain 60 percent.

Wednesday: Sunny with slight chance of thunderstorms early in the morning, then sunny late in the morning. Mostly cloudy with scattered showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 77 to 82 near the shore to around 68 near 5000 feet. North winds around 10 mph shifting to the west in the afternoon. Chance of rain 50 percent.

Waimea

Today: Breezy. Sunny in the morning, then partly sunny with showers likely and slight chance of thunderstorms in the afternoon. Highs around 77 near the shore to 68 to 75 near 3000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Tonight: Breezy. Mostly cloudy with scattered showers and slight chance of thunderstorms. Lows around 60 near the shore to 46 to 54 near 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Wednesday: Mostly cloudy. Scattered showers and slight chance of thunderstorms in the morning, then showers likely and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs around 76 near the shore to 68 to 75 near 3000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

Kohala

Today: Breezy. Sunny in the morning, then partly sunny with showers likely and slight chance of thunderstorms in the afternoon. Highs around 77 near the shore to 68 to 75 near 3000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Tonight: Breezy. Mostly cloudy with scattered showers and slight chance of thunderstorms. Lows around 60 near the shore to 46 to 54 near 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Wednesday: Mostly cloudy. Scattered showers and slight chance of thunderstorms in the morning, then showers likely and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs around 76 near the shore to 68 to 75 near 3000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

South Big Island

Today: Breezy. Sunny in the morning, then cloudy with scattered showers and slight chance of thunderstorms in the afternoon. Highs around 80 near the shore to around 68 near 5000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy early in the evening then becoming mostly clear. Breezy. Scattered showers and slight chance of thunderstorms early in the evening. Lows around 63 near the shore to around 47 near 5000 feet. Northeast winds 10 to 25 mph. Chance of rain 50 percent.

Wednesday: Breezy. Sunny in the morning, then mostly cloudy with scattered showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs around 80 near the shore to around 69 near 5000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Puna

Today: Sunny in the morning, then mostly cloudy with scattered showers and slight chance of thunderstorms in the afternoon. Highs around 79 near the shore to 61 to 67 at 4000 feet. North winds up to 15 mph shifting to the northeast in the afternoon. Chance of rain 50 percent.

Tonight: Mostly cloudy. Showers likely and slight chance of thunderstorms early in the evening, then occasional showers and slight chance of thunderstorms in the late evening and overnight. Lows around 61 near the shore to around 47 at 4000 feet. North winds 10 to 15 mph shifting to the northwest after midnight. Gusts up to 35 mph. Chance of rain 90 percent.

Wednesday: Mostly cloudy. Occasional showers and slight chance of thunderstorms. Locally heavy rainfall possible in the afternoon. Highs around 77 near the shore to 62 to 67 at 4000 feet. West winds 10 to 15 mph shifting to the east in the afternoon. Chance of rain 90 percent.

Waikoloa

Today: Breezy. Sunny in the morning, then partly sunny with scattered showers and slight chance of thunderstorms in the afternoon. Highs 77 to 82 near the shore to 62 to 69 above 4000 feet. Northeast winds up to 15 mph increasing to 10 to 25 mph in the afternoon. Chance of rain 50 percent.

Tonight: Mostly cloudy early in the evening then becoming mostly clear. Breezy. Scattered showers and slight chance of thunderstorms early in the evening, then slight chance of thunderstorms in the late evening and overnight. Lows around 65 near the shore to 43 to 51 above 4000 feet. Northeast winds 10 to 25 mph shifting to the east after midnight. Chance of rain 50 percent.

Wednesday: Sunny with slight chance of thunderstorms in the morning, then partly sunny with scattered showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs around 79 near the shore to 63 to 70 above 4000 feet. East winds 10 to 15 mph shifting to the north in the afternoon. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Moderate to locally breezy trade winds are expected through the upcoming holiday weekend. A period of wetter weather is anticipated the next couple of days as an upper-level low moves over the islands. Showers, some briefly heavy, will favor windward areas, but a few showers can be expected over leeward areas as well. The low will also bring a slight chance of thunderstorms, mainly tonight and Wednesday. The chance for heavy showers will diminish Thursday and Friday.

Discussion

In summary, a period of somewhat wetter weather is possible over the next couple of days as the island atmosphere becomes quite unstable. Some showers could be briefly heavy, with most favoring windward areas, with a slight chance of a thunderstorm popping up just about anywhere. A more stable regime is expected Thursday into Friday. Trade winds of varying speeds and directions are expected into the holiday weekend as a N-S oriented surface trough lingers near the islands.
Latest satellite and radar images indicate a pretty significant decrease in clouds and showers over and around the islands overnight, with just a few showers noted over windward waters. VIIRS imagery showers mostly clear skies over land, except for some layered clouds aloft moving over Kauai from the W. Water vapor imagery (when it was available through 12Z) indicated that a cutoff low aloft to the E of the Big Island was departing to the NE, as a shortwave trough aloft moved over the islands from the NW. The PHTO 12Z sounding continued to indicate an unstable but relatively dry (PWAT of 1.1″) profile over the Big Island, with the instability allowing clouds to extend as high as 20 thousand feet. A more stable profile was depicted by the PHLI 12Z sounding. The short term forecast anticipates abundant sunshine for most areas, a few mainly windward showers, with the Big Island slopes producing clouds, showers and potentially a thunderstorm this afternoon.
A surface trough will linger near and N of the islands for most of the week, with subtle modulations in its position and strength, while strong high pressure persists far to the NE. Moderate to locally breezy trade winds are expected to prevail, with some increase in trade wind speeds expected into tonight. While not all that impactful with regard to the public forecast, there will likely be somewhat difficult-to-predict changes in the direction and strength of the trade winds through the week, with a tendency for NE winds over Kauai and Oahu, and E winds over Maui and the Big Island. This means that incoming moisture will primarily focus over windward areas.
Over the next 24 hours, the low aloft to the E of the islands will continue to weaken and move away to the E, as the trough moving in from the NW helps to form a new cutoff low, this time directly over the islands. 500 mb temperatures over the islands will drop to near -16C, leading to significant destabilization of the island atmosphere. While relatively low PWAT (near 1.1″) may limit shower coverage, some heavier shower cores are expected. A slight chance of thunderstorms is in the Big Island forecast for this afternoon, and for virtually the entire state tonight and Wednesday. Additionally, lower than normal freezing levels means that any upslope precipitation will likely be a wintry mix over the summits and upper slopes of the Big Island, with the potential for dangerous freezing rain/icing over the Haleakala Summit. The low aloft will move NE and away from the islands Wednesday night and Thursday, leading to a gradual increase in stability, and a reduction in shower intensity. A passing shortwave trough may bring a brief period of instability Friday night and Saturday, with the potential for an increase in windward showers.

Aviation

Mostly clear skies and VFR prevail across the islands this morning. Although moderate trades continue to carry pockets of heavy showers toward windward zones, the dry resident airmass is favoring rather limited coverage. At the same time, land breezes have prevented any of these showers from moving onshore. As nocturnal stability erodes during the morning, a more concerted onshore push of isolated to scattered showers over windward areas will be followed by robust afternoon shower development for upslope portions of Leeward Big Island. There, mid-level temperatures will be sufficiently cold to support a slight chance of thunderstorms during peak heating. Isolated thunderstorms will be possible areawide by tonight as a strong upper trough becomes established over the islands. AIRMET Tango for upper turb may be needed by this afternoon as the aforementioned trough deepens over the western end of the state.
No AIRMETs in effect.

Marine

Light to moderate trade winds will hold in place this morning, with the trades strengthening to moderate and locally strong levels this afternoon and tonight. A Small Craft Advisory (SCA) has been issued for the typically windy waters around Maui And the Big Island through 6 AM Wednesday as a result. In addition, a large northwest swell will build seas to the 10 foot SCA threshold for the coastal waters not blocked by the islands, so the SCA also includes many of these marine zones through 6 AM Wednesday.
The trades are expected to ease slightly Wednesday and Wednesday night, but should remain at moderate speeds. A surface trough will then sharpen up over or near the eastern islands Thursday into the weekend, which should shift the trades to a more northeasterly direction and increase speeds back up into the moderate to strong range, especially over the western end of the state. SCA's may once again be needed for portions of the marine area during this time.
An incoming west-northwest swell has arrived in the islands early this morning and based on observations at the NOAA buoys to the distant northwest of the state, will continue to build through the day today. The buoys northwest of the islands indicate that the swell has risen to several feet above predicted levels, and as a result some changes were needed to the ongoing hazards. A High Surf Warning (HSW) is now in effect for north and west facing shores of Niihau, Kauai, and Oahu as well as west facing shores of the Big Island. A High Surf Advisory (HSA) remains in effect for north and west facing shores of Molokai and north facing shores of Maui. The HSW and HSA are both in effect through 6 PM Wednesday. The swell is expected to lower Wednesday night through Friday, but could linger at advisory levels into Wednesday night for exposed north and west facing shores. A new northwest swell is forecast to arrive Friday night, peak below advisory levels Saturday, then lower Saturday night through early next week.
An out of season south swell will will give south shore surf a boost up close to the summertime average today through Thursday. This swell will lower Thursday night and Friday with surf returning to mainly background levels over the weekend into early next week. East shore surf will remain smaller than normal through Wednesday, then rise close to the seasonal average Thursday through the weekend.

HFO Watches/Warnings/Advisories

High Surf Warning until 6 PM HST Wednesday for North and West facing shores of Niihau Kauai and Oahu and for West facing shores of the Big Island.
High Surf Advisory until 6 PM HST Wednesday for North and West facing shores of Molokai and for North facing shores of Maui.
Small Craft Advisory until 6 AM HST Wednesday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Kaiwi Channel, Maui County Windward Waters, Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

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Data Courtesy of NOAA.gov